fix: error when .lua scripts missing in built bundle

lib/commands/index.js

@@ -31,34 +31,32 @@ module.exports = (function() {
     await utils.isRedisReady(client);
     scripts = await (scripts || loadScripts(__dirname));
 
-    return scripts.map(command => {
-      return client.defineCommand(command.name, command.options);
-    });
+    return scripts.map(({ name, options }) => client.defineCommand(name, options));
   };
 })();
 
-function loadScripts(dir) {
-  return _fs
-    .readdirAsync(dir)
-    .then(files => {
-      return files.filter(file => {
-        return path.extname(file) === '.lua';
-      });
-    })
-    .then(files => {
-      return Promise.all(
-        files.map(file => {
-          const longName = path.basename(file, '.lua');
-          const name = longName.split('-')[0];
-          const numberOfKeys = parseInt(longName.split('-')[1]);
-
-          return _fs.readFileAsync(path.join(dir, file)).then(lua => {
-            return {
-              name: name,
-              options: { numberOfKeys: numberOfKeys, lua: lua.toString() }
-            };
-          });
-        })
-      );
-    });
+async function loadScripts(dir) {
+  const scriptsDir = await _fs.readdirAsync(dir);
+  const luaFiles = scriptsDir.filter(file => path.extname(file) === '.lua');
+  if (luaFiles.length === 0) {
+    /**
+     * To prevent unclarified runtime error "updateDelayset is not a function
+     * @see https://github.com/OptimalBits/bull/issues/920
+     */
+    throw new Error('No .lua files found!');
+  }
+  return Promise.all(
+    luaFiles.map(async (file) => {
+      const lua = await _fs.readFileAsync(path.join(dir, file));
+      const longName = path.basename(file, '.lua');
+
+      return {
+        name: longName.split('-')[0],
+        options: {
+          numberOfKeys: parseInt(longName.split('-')[1]),
+          lua: lua.toString(),
+        },
+      };
+    }),
+  );
 }